Fermentable Carbon Sources Research Articles

Enhanced adipic acid production from sugarcane bagasse by a rapid room temperature pretreatment

Adipic acid is an important precursor for manufacturing Nylon-66, and various efficient renewable routes for adipic acid from lignocellulosic biomass are being explored. To effectively valorize biomass into adipic acid, a novel aqueous solution NaOH/ChCl:TH/water (6:24:160, wt/wt/wt) was firstly applied to pretreat sugarcane bagasse (SCB) at a room temperature (25 °C) for a short pretreatment time (1 min) for improving its saccharification efficiency. A deep eutectic solvent ChCl:TH was synthesized by mixing choline chloride (ChCl) and thiourea (TH). The cellulose structure changes of SCB were characterized by FTIR, XRD, SEM, TEM and LSCM. Composition analysis and reducing sugar yield were used to evaluate pretreatment efficiency. Hydrolysis for 72 h, the yields of reducing sugars and glucose from 40 g/L NaOH/ChCl:TH-SCB with complexed cellulases were obtained at 90.2 % and 94.1 %, respectively. Finally, the obtained SCB-hydrolysate was used for adipic acid production by E. coli MG1655 K12. Glucose in SCB-hydrolysate was consumed within 72 h, with a productivity of 0.39 g adipic acid/g glucose, accounting for 72.2 % of the theoretical yield. Further discovery, xylose in SCB-hydrolysate was also consumed for adipic acid fermentation, which contributed to an increase in adipic acid production. In view of transcriptome data, most of the genes involved in carbohydrate metabolism were most significantly up-regulated, which was conductive to improve the yield of adipic acid using biomass-hydrolysate as carbon source. Therefore, the NaOH/ChCl:TH-SCB hydrolysates were a better carbon source for adipic acid fermentation compared to commercial glucose. Obviously, this established rapid room temperature pretreatment with NaOH/ChCl:TH was proven to be effective for enhancing saccharification efficiency of SCB, and the hydrolysates had excellent adipic acid fermentability.

Role of ROX1, SKN7, and YAP6 Stress Transcription Factors in the Production of Secondary Metabolites in Xanthophyllomyces dendrorhous.

Xanthophyllomyces dendrorhous is a natural source of astaxanthin and mycosporines. This yeast has been isolated from high and cold mountainous regions around the world, and the production of these secondary metabolites may be a survival strategy against the stress conditions present in its environment. Biosynthesis of astaxanthin is regulated by catabolic repression through the interaction between MIG1 and corepressor CYC8–TUP1. To evaluate the role of the stress-associated transcription factors SKN7, ROX1, and YAP6, we employed an omic and phenotypic approach. Null mutants were constructed and grown in two fermentable carbon sources. The yeast proteome and transcriptome were quantified by iTRAQ and RNA-seq, respectively. The total carotenoid, sterol, and mycosporine contents were determined and compared to the wild-type strain. Each mutant strain showed significant metabolic changes compared to the wild type that were correlated to its phenotype. In a metabolic context, the principal pathways affected were glycolysis/gluconeogenesis, the pentose phosphate (PP) pathway, and the citrate (TCA) cycle. Additionally, fatty acid synthesis was affected. The absence of ROX1 generated a significant decline in carotenoid production. In contrast, a rise in mycosporine and sterol synthesis was shown in the absence of the transcription factors SKN7 and YAP6, respectively.

Characterizing phenotypic diversity of trehalose biosynthesis mutants in multiple wild strains of Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, trehalose-6-phospahte synthase (Tps1) and trehalose-6-phosphate phosphatase (Tps2) are the main proteins catalyzing intracellular trehalose production. In addition to Tps1 and Tps2, 2 putative regulatory proteins with less clearly defined roles also appear to be involved with trehalose production, Tps3 and Tsl1. While this pathway has been extensively studied in laboratory strains of S. cerevisiae, we sought to examine the phenotypic consequences of disrupting these genes in wild strains. Here we deleted the TPS1, TPS2, TPS3, and TSL1 genes in 4 wild strains and 1 laboratory strain for comparison. Although some tested phenotypes were not shared between all strains, deletion of TPS1 abolished intracellular trehalose, caused inability to grow on fermentable carbon sources and resulted in severe sporulation deficiency for all 5 strains. After examining tps1 mutant strains expressing catalytically inactive variants of Tps1, our results indicate that Tps1, independent of trehalose production, is a key component for yeast survival in response to heat stress, for regulating sporulation, and growth on fermentable sugars. All tps2Δ mutants exhibited growth impairment on nonfermentable carbon sources, whereas variations were observed in trehalose synthesis, thermosensitivity and sporulation efficiency. tps3Δ and tsl1Δ mutants exhibited mild or no phenotypic disparity from their isogenic wild type although double mutants tps3Δ tsl1Δ decreased the amount of intracellular trehalose production in all 5 strains by 17-45%. Altogether, we evaluated, confirmed, and expanded the phenotypic characteristics associated trehalose biosynthesis mutants. We also identified natural phenotypic variants in multiple strains that could be used to genetically dissect the basis of these traits and then develop mechanistic models connecting trehalose metabolism to diverse cellular processes.

Direct production of polyhydroxybutyrate and alginate from crude glycerol by Azotobacter vinelandii using atmospheric nitrogen

While biodiesel is drawing attention as an eco-friendly fuel, the use of crude glycerol, a byproduct of the fuel production process, has increasingly become a concern to be addressed. Here we show the development of a low-cost fermentation technology using an atmospheric nitrogen-fixing bacterium to recycle crude glycerol into functional biopolymers. Azotobacter vinelandii showed substantial growth on tap water-diluted crude glycerol without any pretreatment. The number of viable A. vinelandii cells increased over 1000-fold under optimal growth conditions. Most of the glycerol content (~ 0.2%) in the crude glycerol medium was completely depleted within 48 h of culture. Useful polymers, such as polyhydroxybutyrate and alginate, were also produced. Polyhydroxybutyrate productivity was increased ten-fold by blocking the alginate synthesis pathway. Although there are few examples of using crude glycerol directly as a carbon source for microbial fermentation, there are no reports on the use of crude glycerol without the addition of a nitrogen source. This study demonstrated that it is possible to develop a technology to produce industrially useful polymers from crude glycerol through energy-saving and energy-efficient fermentation using the atmospheric nitrogen-fixing microorganism A. vinelandii.

Fermentation of Trichoderma Reesei PKJ and Aspergillus Niger FNCC 6 to Improve the Production of Fermentable Sugar from Sago Meal

"Lignocellulosic compounds from sago waste are abundant, inexpensive, untapped carbon sources, and even tend to pollute the environment. Trichoderma reesei and Aspergillus niger are two fungi that are widely used to degrade lignocellulose compounds into simple sugars. T. reesei plays the first role to degrade cellulose. Then A niger will play a role in continuing the process of changing the product of cellulose degradation into simple sugars. The right combination of time to inoculate A. niger into media after T. reesei growing in could maximize the degradation process of lignocellulose compounds. In this study, T. reesei Pk1J2 inoculation was carried out 48 hours before the A. niger FNCC 6114 inoculation. Fermentation was continued in 48 h (total 96 h). The result is that the production of fermentable sugar increases 3-5 times compared to only using monoculture of T reesei or A.niger. Thus, this combination can be recommended for the preparation of potential carbon sources for fermentation and industrialization."

Sequential Dark-Photo Batch Fermentation and Kinetic Modelling for Biohydrogen Production Using Cheese Whey as a Feedstock.

The present work describes the utilisation of cheese whey to produce biohydrogen by sequential dark-photo fermentation. In first stage, cheese whey was fermented by Enterobacter aerogenes 2822 cells in a 2 L double-walled cylindrical bioreactor to produce hydrogen/organic acids giving maximum biohydrogen yield and cumulative hydrogen of 2.43 ± 0.12molmol-1 lactose and 3270 ± 143.5mL at cheese whey concentration of 105mM lactose L-1. The soluble metabolites of dark fermentation when utilised as carbon source for photo fermentation by Rhodobacter sphaeroides O.U.001, the yield, and cumulative hydrogen was increased to 4.22 ± 0.20molmol-1 VFA and 3800 ± 170mL, respectively. Meanwhile, an overall COD removal of about 38.08% was also achieved. The overall biohydrogen yield was increased from 2.43 (dark fermentation) to 6.65 ± 0.25molmol-1 lactose. Similarly, the modelling for biohydrogen production in bioreactor was done using modified Gompertz equation and Leudeking-Piret model, which gave adequate simulated fitting with the experimental values. The carbon material balance showed that acetic acid, lactic acid, and CO2 along with microbial biomass were the main by-products of dark fermentation and comprised more than 75% of carbon consumed.

Halomonas uses short-chain fatty acids to synthesize polyhydroxyalkanoates

Halomonas can grow on diverse carbon sources. As it can be used for unsterile fermentation under high-salt conditions, it has been applied as a chassis for next-generation industrial biotechnology. Short-chain volatile fatty acids, including acetate, propionate, and butyrate, can be prepared from biomass and are expected to be novel carbon sources for microbial fermentation. Halomonas sp. TD01 and TD08 were subjected to shaking culture with 10-50 g/L butyrate, and they were found to effectively synthesize poly-3-hydroxybutyrate with butyrate as the carbon source. The highest yield of poly-3-hydroxybutyrate was achieved at butyrate concentration of 20 g/L (9.12 g/L and 7.37 g/L, respectively). Butyrate at the concentration > 20 g/L inhibited cell growth, and the yield of poly-3-hydroxybutyrate decreased to < 4 g/L when butyrate concentration was 50 g/L. Moreover, Halomonas sp. TD08 can accumulate the copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate by using propionate and butyrate as carbon sources. However, propionate was toxic to cells. To be specific, when 2 g/L propionate and 20 g/L butyrate were simultaneously provided, cell dry weight and polymer titer were 0.83 g/L and 0.15 g/L, respectively. The addition of glycerol significantly improved cell growth and boosted the copolymer titer to 3.95 g/L, with 3-hydroxyvalerate monomer content of 8.76 mol%. Short-chain volatile fatty acids would be promising carbon sources for the production of polyhydroxyalkanoates by Halomonas.

Ethanol Productivity of Ethanol-Tolerant Mutant Strain Pichia kudriavzevii R-T3 in Monoculture and Co-culture Fermentation with Saccharomyces cerevisiae

We previously developed ethanol-tolerant P. kudriavzevii R-T3 (P.ku R-T3) mutant from its parental strain P.ku R-WT by evolutionary adaptation method. Hence, we further analyze the ethanol productivity of the particular isolates in a monoculture and co-culture with industrial yeast Saccharomyces cerevisiae BY4741 at various inoculum ratio. Based on the spot assay, R3 mutant yeast showed better cell viability under 10% ethanol stress than the wild type, potentially due to the high expression level of PKINO1 gene involved in the synthesis of inositol. In the monoculture fermentation, S. cerevisiae could use glucose, while P.ku could use mixed glucose and xylose as carbon sources for ethanol fermentation. P.ku R-T3 performed the most potential ethanol kinetics parameters, including the highest ethanol production (10.10 g/L), ethanol productivity (0.21 g/L/h), and fermentation efficiency (84.36%). Upscaling the inoculum of P.ku R-T3 by ten times resulted in 10% higher ethanol production. However, the highest substrate utilization rate did not indicate an increase in ethanol production. Indeed, P.ku R-T3 showed a low mixed substrate use but produced higher ethanol production than S. cerevisiae, as much as 21-31%, depending on the initial inoculum. Interestingly, the co-culture of P.ku R-T3 and BY4741 did not substantially produce higher ethanol production than the monoculture technique. About 30% reduction of ethanol production was found by co-culturing BY4741 with P.ku R-T3 than P.ku R-T3 alone. Taken together, the monoculture fermentation of P.ku R-T3 remains the promising fermentation technique than that of the co-culture with industrial yeast S. cerevisiae.

Deciphering functional redundancy and energetics of malate oxidation in mycobacteria

Oxidation of malate to oxaloacetate, catalyzed by either malate dehydrogenase (Mdh) or malate quinone oxidoreductase (Mqo), is a critical step of the tricarboxylic acid cycle. Both Mqo and Mdh are found in most bacterial genomes, but the level of functional redundancy between these enzymes remains unclear. A bioinformatic survey revealed that Mqo was not as widespread as Mdh in bacteria but that it was highly conserved in mycobacteria. We therefore used mycobacteria as a model genera to study the functional role(s) of Mqo and its redundancy with Mdh. We deleted mqo from the environmental saprophyte Mycobacterium smegmatis, which lacks Mdh, and found that Mqo was essential for growth on nonfermentable carbon sources. On fermentable carbon sources, the Δmqo mutant exhibited delayed growth and lowered oxygen consumption and secreted malate and fumarate as terminal end products. Furthermore, heterologous expression of Mdh from the pathogenic species Mycobacterium tuberculosis shortened the delayed growth on fermentable carbon sources and restored growth on nonfermentable carbon sources at a reduced growth rate. In M. tuberculosis, CRISPR interference of either mdh or mqo expression resulted in a slower growth rate compared to controls, which was further inhibited when both genes were knocked down simultaneously. These data reveal that exergonic Mqo activity powers mycobacterial growth under nonenergy limiting conditions and that endergonic Mdh activity complements Mqo activity, but at an energetic cost for mycobacterial growth. We propose Mdh is maintained in slow-growing mycobacterial pathogens for use under conditions such as hypoxia that require reductive tricarboxylic acid cycle activity.

A novel transcriptional activation mechanism of inulinase gene in Kluyveromyces marxianus involving a glycolysis regulator KmGcr1p with unique and functional Q-rich repeats.

Kluyveromyces marxianus is the most suitable fungus for inulinase industrial production. However, the underlying transcriptional activation mechanism of the inulinase gene (INU1) is hitherto unclear. Here, we undertook genetic and biochemical analyses to elucidate that a glycolysis regulator KmGcr1p with unique Q-rich repeats is the key transcriptional activator of INU1. We determined that INU1 and glycolytic genes share similar transcriptional activation patterns and that inulinase activity is induced by fermentable carbon sources including the hydrolysis products of inulin (fructose and glucose), which suggests a novel model of product feedback activation. Furthermore, all four CT-boxes in the INU1 promoter are important for KmGcr1p DNA-binding in vitro, but the most downstream CT-box 1 primarily confers upstream activating sequence activity in vivo. More intriguingly, the use of artificial and natural GCR1 mutants suggests that the Q-rich repeats act as a functional module to maintain KmGcr1p transcriptional activity by contributing to its solubility and DNA-binding affinity. Altogether, this study uncovers a novel transcriptional activation mechanism for the inulinase gene, that is different from the previous understanding for filamentous fungi, but might have universal significance among inulinase-producing yeasts, thereby leading to a better understanding of the regulation mechanism of yeast inulinase genes.

Potential of a year-round, closed-loop process for volatile organic compounds reduction in pinewood strands by Pseudomonas putida PX1 cultivated in seasonally varying process effluents

Sustainable utilization of waste streams from bioresources is a challenging opportunity for the future. This study investigated the potential of a seasonally varying process effluent stream from medium-density fiberboard production for a year-round cultivation process of Pseudomonas putida PX1 for reduction of volatile organic compounds (VOC) in pinewood strands. For four years, seasonal variations with abundant fermentable carbon sources during colder periods and few carbon sources during warmer periods were observed. Nitrogen sources present in process effluent required for optimal biomass production are insufficient when abundant carbon sources are available and should be supplemented. VOC reduction in pinewood strands with P. putida after mixed substrate fermentation showed very promising results for industrial applications. Total VOC emissions were reduced by more than 55% in only 3 h. Most aldehydes and terpenes were effectively reduced by 67%–100%, except for Δ-3-carene and α-terpinolene, which were reduced by 20%–22%.

Screening of cellulase-producing bacteria and their effect on the chemical composition and aroma quality improvement of cigar wrapper leaves

A high yield cellulase production strain was screened from the surface of cigar wrapper leaves and added to cigar wrapper leaves for fermentation in the present study. The enzyme-producing strain was identified as Bacillus velezensis, and its maximum carboxymethyl cellulase activity could reach 44.3 U/mL. Making the cellulose degradation rate of cigar wrapper leaves as the index, the fermentation temperature, inoculum concentration, and carbon and nitrogen source addition concentration were optimized by response surface methodology. The results showed that under the conditions of inoculation concentration of 20%, fermentation temperature of 37 °C, addition of 4.5 ‰ glucose and 2.25 ‰ glutamate, the highest degradation rate of tobacco cellulose was 31.7%. Significance analysis results showed that the order of factors affecting the degradation rate of cigar wrapper cellulose was: inoculation concentration &gt; carbon and nitrogen source addition concentration &gt; temperature. The analysis of aroma substances under the optimal conditions found that the total amount of aroma substances of cigar wrapper increased by 26.1% compared with that before fermentation, in which β-damascenone, megastigmatrienone, farnesyl acetone, and solanone were significantly improved. The results were conducive to improving the aroma quality and concentration of cigar wrapper leaves.

Genomic and Metabolic Features of an Unexpectedly Predominant, Thermophilic, Assistant Starter Microorganism, Thermus thermophilus, in Chinese Inner Mongolian Cheese.

Inner Mongolian cheese is a traditional dairy product in China. It is produced without rennet, using naturally acidified milk that is simmered to achieve whey separation. In order to analyse the impact of simmering on the microbial community structure, high-throughput sequencing was performed to obtain bacterial 16S rRNA sequences from cheeses from the Ordos (ES), Ulanqab (WS), Horqin (KS) and Xilingol (XS) grasslands of Inner Mongolia. The relative abundance of an unexpected microorganism, Thermus thermophilus, ranged from 2% to 9%, which meant that its dominance was second only to that of lactic acid bacteria (LABs). Genome sequencing and fermentation validation were performed in T. thermophilus N-1 isolated from the Ordos, and it was determined that T. thermophilus N-1 could ingest and metabolise lactose in milk to produce lactate during the simmering process. T. thermophilus N-1 could also produce acetate, propionate, citrate and other organic acids through a unique acetate production pathway and a complete propionate production pathway and TCA cycle, which may affect texture and flavour development in Inner Mongolian cheese. Simultaneously, the large amount of citrate produced by T. thermophilus N-1 provides a necessary carbon source for continuous fermentation by LABs after the simmering step. Therefore, T. thermophilus N-1 contributes to cheese fermentation as a predominant, thermophilic, assistant starter microorganism unique to Chinese Inner Mongolian cheese.

Novel Propagation Strategy of Saccharomyces cerevisiae for Enhanced Xylose Metabolism during Fermentation on Softwood Hydrolysate

An economically viable production of second-generation bioethanol by recombinant xylose-fermenting Saccharomyces cerevisiae requires higher xylose fermentation rates and improved glucose–xylose co-consumption. Moreover, xylose-fermenting S. cerevisiae recognises xylose as a non-fermentable rather than a fermentable carbon source, which might partly explain why xylose is not fermented into ethanol as efficiently as glucose. This study proposes propagating S. cerevisiae on non-fermentable carbon sources to enhance xylose metabolism during fermentation. When compared to yeast grown on sucrose, cells propagated on a mix of ethanol and glycerol in shake flasks showed up to 50% higher xylose utilisation rate (in a defined xylose medium) and a double maximum fermentation rate, together with an improved C5/C6 co-consumption (on an industrial softwood hydrolysate). Based on these results, an automated propagation protocol was developed, using a fed-batch approach and the respiratory quotient to guide the ethanol and glycerol-containing feed. This successfully produced 71.29 ± 0.91 g/L yeast with an average productivity of 1.03 ± 0.05 g/L/h. These empirical findings provide the basis for the design of a simple, yet effective yeast production strategy to be used in the second-generation bioethanol industry for increased fermentation efficiency.

Adaptive laboratory evolution of Escherichia coli W enhances gamma-aminobutyric acid production using glycerol as the carbon source

The microbial conversion of glycerol into value-added commodity products has emerged as an attractive means to meet the demands of biosustainability. However, glycerol is a non-preferential carbon source for productive fermentation because of its low energy density. We employed evolutionary and metabolic engineering in tandem to construct an Escherichia coli strain with improved GABA production using glycerol as the feedstock carbon. Adaptive evolution of E. coli W under glycerol-limited conditions for 1300 generations harnessed an adapted strain with a metabolic system optimized for glycerol utilization. Mutation profiling, enzyme kinetic assays, and transcriptome analysis of the adapted strain allowed us to decipher the basis of glycerol adaptation at the molecular level. Importantly, increased substrate influx mediated by the mutant glpK and modulation of intracellular cAMP levels were the key drivers of improved fitness in the glycerol-limited condition. Leveraging the enhanced capability of glycerol utilization in the strain, we constructed a GABA-producing E. coli W-derivative with superior GABA production compared to the wild-type. Furthermore, rationally designed inactivation of the non-essential metabolic genes, including ackA, mgsA, and gabT, in the glycerol-adapted strain improved the final GABA titer and specific productivity by 3.9- and 4.3-fold, respectively, compared with the wild-type.

An innovative strategy of recycling miscellaneous waste carbohydrates from high-fructose syrup production for Pichia pastoris fermentation

Recycling waste carbon source for fermentation is of great interests and high practical value. However, the process suffered some problems like unclear carbohydrate composition, low nutrition content, presence of various contaminants and high cost for pretreatment. Currently, the high-fructose syrup (HFS) production industry in China generates a large amount of waste liquid containing miscellaneous waste carbohydrates (MWC), which has a notable environmental impact. To recycle MWC for Pichia pastoris fermentation, the composition of MWC was analyzed and the fermentation processes were optimized. The composition of MWC was determined as 802.3 g L−1 total carbohydrate, 480 g L−1 glucose, 92 g L−1 fructose, 103.6 g L−1 maltose, 36.8 g L−1 maltotriose and 89.9 g L−1 other oligosaccharides with different degrees of polymerization (DPs 4–16). After the fermentation medium and conditions for pGAP/pAOX1-P. pastoris were optimized, MWC were employed as the alternative carbon source to culture the two strains to produce endo-β-1,3-glucanase in 7-L bioreactors. Using MWC for pGAP-P. pastoris culture, the dry cell weight (DCW) and endo-β-1,3-glucanase activity reached 69.1 g L−1 and 171.8 U mL−1, respectively, which were the same levels as in the batch using glucose as the carbon source. When using MWC and the self-designed DO-Stat-Time feeding strategy for pAOX1-P. pastoris culture, the maximum DCW and enzyme activity reached 83.6 g L−1 and 212.3 U mL−1, which improved 41.4% and 34.9%, respectively compared with the control group. This study established cleaner production procedures for both HFS and P. pastoris fermentation industries by considerably reducing environmental pollution and decreasing the production cost.

New trends in bioprocesses for lignocellulosic biomass and CO2 utilization

Innovation and technology are seen today as key points in the transition to a greener and more sustainable economy. In this sense, the development of new processes able to result in reduced emissions and levels of CO2 in the atmosphere has been considered essential to support this transition and, at the same time, promote economic growth. Several techno-economic and life cycle assessment studies have shown promising data when sugars derived from lignocellulosic biomass are used as carbon source for fermentation processes. The use of CO2 as carbon source for fermentation is another smart concept for reusing this molecule while minimizing its emissions to the atmosphere. However, the large-scale implementation of biomass-based and CO2-based processes still require significant research efforts to result in robust and cost-competitive technologies. This paper discusses some promising approaches able to advance this research area including potential strategies for process intensification (enzymatic hydrolysis using high solid loading, simultaneous saccharification and fermentation, fermentation with downstream process integration), robust microbial strains for application in biomass-based and CO2-based bioprocesses, microbial co-cultivation systems, greener technologies for lignocellulosic biomass fractionation, among others. A critical evaluation of sustainability aspects including techno-economic and life cycle assessment is also provided. Overall, this study contributes with information on innovative trends able to advance the development of greener bioprocesses.

Bioethanol Production and Proximate Compostion of Waste Potatoes

Bioethanol can be produced from biological matter through processing of food wastes or crops meant for bioethanol production. This study used potato wastes from food vendors in Sokoto, Nigeria as a cheap and renewable carbon source for fermentation of ethanol. Saccharomyces cerevisiae was used to optimize the growth parameters and hydrolysis of potato wastes of the ethanol fermentation aimed at achieving maximum production of bioethanol. Following the analysis, results indicated that, a combination of 0.5, 1.0, 1.5, 2.0, 2.5% of H2SO4 at 121˚C for 20 min in an autoclave can yield complete hydrolysis of all starch contents of potato wastes. The average proximate composition of the potato wastes showed 13.94%,1.42%, 1.72%,1.38%,0.43% and 81.11% of Moisture, Ash, Fat, Crude protein, Fiber and Carbohydrate contents respectively. Positive confirmation of reducing sugars and bioethanol was achieved by using benedicts and Jones’ reagents respectively, Quantitative Test for reducing sugars indicated 124.9 mg/gm, 88.6 mg/gm, 61.45 mg/gm, 53.22 mg/gm, 47.23 mg/gm for 0.5%, 1.5%, 2.0%,2.5% and 3% concentrations respectively.

No re-calibration required? Stability of a bioelectrochemical sensor for biodegradable organic matter over 800 days

Microbial Fuel Cells (MFCs) operated as biosensors could potentially enable truly low-cost, real-time monitoring of organic loading in wastewaters. The current generated by MFCs has been correlated with conventional measures of organic load such as Biochemical Oxygen Demand (BOD), but much remains to be established in terms of the reliability and applicability of such sensors. In this study, batch-mode and multi-stage, flow-mode MFCs were operated for over 800 days and regularly re-calibrated with synthetic wastewater containing glucose and glutamic acid (GGA). BOD5 calibration curves were obtained by normalising the current measured as a percentage of maximum current. There was little drift between recalibrations and non-linear Hill models of the combined dataset had R2 of 88–95%, exhibiting a stable response over time and across devices. Nonetheless, factors which do affect calibration were also assessed. Increasing external resistance (from 43.5 to 5100 Ω) above the internal resistance determined by polarisation curve decreased the calibration upper limit from 240 to 30 mg/l O2 BOD5. Furthermore, more fermentable carbon sources increased the detection range, as tested with samples of real wastewater and synthetic media containing GGA, glucose-only and glutamic acid-only. Biofilm acclimatisation therefore did not account for differences between aerobic oxygen demand determinations and anaerobic MFC responses; these are likely attributable to competitive processes such as fermentation. This further highlights the potential for MFCs as real-time sensors for organic load monitoring and process control in addition to BOD-compliant measurement systems.

Production of fuel grade anhydrous ethanol: a review

Alcoholic fermentation of fermentable carbon sources like molasses and table sugar using yeast are typical route in producing alcohol particularly known as bioethanol (C2H5OH). The key challenge encountered in bioethanol production process is to eliminate the impurity presence within the bioethanol which mainly water. Distillation is an energy extensive process which commonly used to recover ethanol up to 95% purity due to the presence of azeotropic composition. The distillation will no longer appropriate for further purification once the azeotrope composition has reached. Nonetheless, to be able to use as a viable fuel for gasoline engine or for any other utilizations where the purity is a major concern, further dehydration steps are needed producing an absolute ethanol. Few studies have been investigated on various dehydration methods for producing anhydrous ethanol, including azeotropic distillation, extractive distillation, adsorption, membrane pervaporation, and solvent extraction process. This review offers an insight into currently used technology on the ethanol dehydration methods and the future prospect on the continuous improvement particularly on the process energy requirement and efficiency will be discussed.